The present invention relates to a switching mechanism for a circuit breaker, such as a molded circuit breaker for wiring and earth leakage breaker, and in particular, to a switching mechanism for the circuit breaker to reduce an operating space.
FIG. 6 is a vertical sectional view showing a general configuration of a conventional switching mechanism for a three-pole circuit breaker in a closed-circuit state, and FIG. 7 is a top view of a main portion of the switching mechanism of FIG. 6. In these figures, the switching mechanism has a latch 4 having one end rotatably supported by a latch shaft 3 on one of a laterally disposed pair of side plates of a frame 2 fixed to a case 1 of a circuit breaker body, and the other end generally engaging a latch receiver (not shown); a holder 7 made of an insulating material for holding a movable contact 5 and rotatably supported on the case 1 via an integral switching shaft 6; a gate-shaped handle lever 10 rockably supported on the side plates of the frame 2 around lever shafts 8 and having a switching handle 9 installed at its head; a toggle link 16 consisting of a laterally disposed pair of first and second links 12, 13, with ends of the first and second links 12, 13 being connected together by a toggle shaft 11, a free end of the first link 12 being connected to the latch 4 by a shaft 14 and a free end of the second link 13 being connected to the holder 7 by a shaft 15; and a laterally disposed pair of switching springs 17, each being stretched between the toggle shaft 11 and the head of the handle lever 10.
In the illustrated closed state, due to the tension of the switching springs 17 on the toggle shaft 11, the toggle link 16 extends in such a way that an axis 18 joining the connection point (central point of the shaft 14) between the first link 12 and the latch 4 with the central point of the toggle shaft 11 is nearly linear with an axis 19 joining the connection point (central point of the shaft 15) between the second link 13 and the holder 7 with the central point of the toggle shaft 11. The holder 7 is subjected to a counterclockwise rotational force in FIG. 6 around the switching shaft 6, thereby pressing the movable contact 5 against a fixed contact shoe 20.
When the switching handle 9 is gripped to rotate the handle lever 10 clockwise in FIG. 6, the effect of the switching springs 17 on the toggle link 16 is inverted at a dead point at which an axis 22 passes the axis 18 of the first link 12 from left to right, wherein the axis 22 is a line joining the connection point 21 between one switching spring 17 and the handle lever 10 with the central point of the toggle shaft 11. Thus, the toggle link 16 is bent in a V-shape at the end of the handle lever 10, and the holder 7 is rotationally driven clockwise in FIG. 6 to separate the movable contact 5 from a fixed contact 20 (opening operation). In addition, in this open-circuit state, when the handle lever 10 is rotationally operated counterclockwise, the effect of the switching spring 17 is reversed at the dead point at which the axis 22 of the switching spring 17 passes the axis 18 of the first link 12 from right to left. The movable contact 5 is then contacted with the fixed contact 20 as shown in the figure (closing operation).
Furthermore, when a current flowing through the circuit breaker becomes excessive to activate an overcurrent trip apparatus (not shown), the latch 4 is disengaged from the latch receiver to rotate the latch 4 urged by the switching springs 17 via the first link 12 counterclockwise in FIG. 6 around the latch shaft 3. As a result, the effect of the switching springs 17 on the toggle link 16 is inverted at the dead point at which the axis 18 passes the axis 22 from right to left. The toggle link 16 is then bent in the V-shape to rotationally drive the holder 7 clockwise in FIG. 6, thereby separating the movable contact 5 from the fixed contact 20 (tripping operation).
In the conventional switching mechanism, the connection point between the first link 12 and the latch 4 is located in a nearly opposite position relative to the connection point between the second link 13 and the holder 7 with respect the toggle shaft 11. Thus, when the toggle link 16 is straightened, the height of the mechanism increases, and when the link 16 is bent, the movement range of the first and second links 12 and 13 is wide. Thus, the reduction of the installation space is very difficult.
It is an object of this invention to reduce the installation space for the switching mechanism in order to miniaturize the circuit breaker.